1. Field of the Invention
The present invention relates to a process for the preparation of a difluorohalomethoxybenzene.
2. Prior Art of the Invention
Difluorohalomethoxybenzene derivatives, e.g., those having the formula (I) below, are generally used for compounds having herbicidal activity or pharmacological activity and intermediates for the preparation of compounds having these activities. These derivatives can also be utilized as important intermediates in organic synthesis and are hence very valuable compounds in industry.
Particularly, 3-phenoxybenzyl 2-(4-bromodifluoromethoxyphenyl)-2-methylpropyl ether or 1-(3-phenoxyphenyl)-4-(4-bromodifluoromethoxyphenyl)-4-methylpentane, viz., compounds of Formula (III) wherein Z is Br, Y is H and A is an oxygen atom (VII) or a methylene group (VIII), respectively, are known to have a high insecticidal and acaricidal action (Japanese Patent Laid-Open Publication No. SHO 63-45233 (1988). ##STR1##
It is conventionally known that the difluorohalomethoxybenzene derivatives having the formula (I) below can be prepared from the reaction of a metal phenolate having the formula (II) below with dibromodifluoromethane or bromochlorodifluoromethane.
The bromodifluoromethoxylation of phenol or substituted phenols is disclosed in the following references:
1) Japanese Patent Laid-Open Publication No. SHO 58-128334 (1983) has examples for the bromodifluoromethoxylation of the substituted phenols.
According to this reference, 1 mole of sodium salt of p-hydroxybenzo-nitrile and 1.7 moles of dibromodifluoromethane are dissolved in dimethylformamide, stirred at the room temperature for a day and distilled to obtain desired p-(bromodifluoromethoxy)-benzonitrile. However, the yield is only about 31.8%.
2) Japanese Patent Laid-Open Publication No. SHO 57-109737 (1982) discloses examples for bromodifluoromethoxylation of the substituted phenols.
According to the process, 0.1 mole of potassium salt of p-cresol is dissolved in dimethylformamide, a catalytic amount of propanethiol is added, dibromodifluoromethane is further added, and reacted at 20.degree. to 30.degree. C. for 4 hours to obtain p-(bromodifluoromethoxy) toluene in a 21% yield.
3) According to the Journal of Fluorine Chemistry, 20, 765 (1982), o-allylphenol is dissolved in dimethylformamide, an equimolar amount of potassium hydroxide and a catalytic amount of 18-crownether-6 are added and then 2 moles of dibromodifluoromethane per mole of o-allylphenol is added. The mixture is reacted to obtain the corresponding o-(bromodifluoromethoxy)allylbenzene in a 9% yield.
4) In Tetrahedron, 37, 4209(1981), the reaction of various substituted phenols with dibromodifluoromethane are described. For example, the potassium salt of phenol is dissolved in dimethylformamide, a catalytic amount of propanethiol is added and then twice by weight of dibromodifluoromethane per weight of the potassium salt of phenol is added. The mixture is reacted to obtain the corresponding bromodifluoromethoxybenzene in a 9% yield.
Examples of the same procedures using 4-methoxyphenol, p-cresol, 4 chlorophenol and 4-nitrophenol are also described, 4-(bromodifluoromethoxy)anisole, 4-(bromodifluoromethoxy)toluene, 4-(bromodifluoromethoxy)chlorobenzene, and 4-(bromodifluoromethoxy)-nitrobenzene are obtained in the yield of 1.5%, 4%, 16% and 25%, respectively.
5) In Tetrahedron Letters, 22, 328(1981), potassium salt of phenol is dissolved in dimethylformamide, twice by mole of dibromodifluoromethane per mole of the potassium salt of phenol is added, and the mixture is reacted to obtain corresponding bromodifluoromethoxybenzene in about 9% yield.
A process for the preparation of the compounds having the above formula (VII) and formula (VIII) is also disclosed in Japanese Patent Laid-Open Publication No. SHO 63-45233(1983). 1-(3-Phenoxyphenyl)-4-(hydroxyphenyl)-4-methylpentane or 3-phenoxybenzyl 2-(4-hydroxyphenyl)-2-methylpropyl ether is dissolved in N,N'-dimethylimidazolidinone in combination with a 2 mole ratio of potassium tert-butoxide. The thus obtained solution is added dropwise at 60.degree. C. to a solution containing 5 mole ratio of dibromodifluoromethane in N,N'-dimethylimidazolidinone. The resulting mixture is further reacted for 3 hours at the same temperature. The desired bromodifluoromethoxy compound is isolated by column chromatography. However, the yields are only about 46%.
As mentioned above, the known processes for reacting phenol or substituted phenols with dibromodifluoromethane to obtain the corresponding bromodifluoromethyl ethers provide only a low yield of the desired product.